Viewpoint : Abdominal aortic aneurysm

The definition of an aneurysm is when a blood vessel increases by more than 50% in diameter. In the aorta, which has an average diameter of 2cm, anything measuring 3cm and above is by definition an aneurysm. Abdominal aortic aneurysm (AAA) is the 13th most common cause of male deaths in the world.

The most important association with an AAA is high BP, which is also an independent risk factor. Other risk factors include smoking, male gender (men are on average four times more likely to develop AAA than women) and genetic factors (a positive family history for AAA).

Typically, an AAA is most often seen in men over the age of 60 years who have one or more of the above-mentioned risk factors.

The larger the aneurysm, the more likely it is to rupture and cause catastrophic internal bleeding, which invariably leads to death. It is therefore important to try to identify an AAA before it ruptures.

Symptoms of rupture

Sudden-onset severe back pain - may radiate to buttocks and legs; may be felt in abdomen

Dizziness or nausea

Feeling clammy

Hypertension

Tachycardia

Features of shock

Tender pulsatile abdominal mass or stiff and ridged abdomen

Symptoms

AAAs tend to develop over a number of years and do not usually cause any symptoms until they rupture. However, a number of patients will present with abdominal or more commonly back pain, which may be present for a few days or weeks.

This suggests stretching of the abdominal aorta, which tends to indicate a pre-rupture situation. Such a presentation should prompt urgent referral to the vascular service or, on occasion, A&E.

The symptoms most commonly associated with a ruptured AAA include sudden-onset severe back pain, which can radiate to the buttocks and legs and is sometimes felt in the abdomen. The patient may feel dizzy or nauseated.

On examination, they may be clammy, hypertensive, tachycardic and exhibiting features of shock. Abdominal examination may reveal a tender pulsatile mass or a stiff and ridged abdomen. Any of these features would prompt an emergency referral to hospital.

Investigations

Identifying a patient with a pulsatile mass should prompt assessment with an abdominal ultrasound scan, the simplest test to diagnose AAA.

More detailed investigation would involve a CT angiogram of the aorta, which is normally requested by the vascular surgeon to clarify the morphology of the aneurysm and confirm the best treatment option.

Generally, an AAA that is smaller than 5cm in maximum diameter will be managed by serial ultrasound scans unless it is rapidly expanding or is symptomatic, in which case it will be treated surgically.

Aneurysms of 5cm or above are generally treated with surgery.

Treatment

For many years, the gold standard treatment for patients with AAA has been open surgical repair.

However, since the early 1990s, endovascular repair has become the preferred treatment in most cases. This is a keyhole procedure, in which stent grafts are passed through the femoral arteries in the groin and deployed into the abdomen to exclude the aortic aneurysm.

This type of procedure is associated with a lower rate of in-hospital morbidity and mortality.

Outcomes of AAA repair

In the elective scenario, the outcomes of endovascular repair and open surgery tend to be excellent.

The overall mortality of such procedures is less than 5% and in clinical centres of excellence, endovascular repair may be associated with a mortality rate of less than 1%.

However, about 90% of patients whose aneurysm has ruptured will not reach hospital alive and about 30% of those who do will die during or after surgery.

It is important to identify those aneurysms before they rupture. Considering that they are relatively common and generally do not cause any symptoms until it is too late, a number of screening programmes have been developed to identify the condition early.

Screening programme

Since 2009, a national NHS Abdominal Aortic Aneurysm Screening Programme has gradually been introduced across England.

This involves a one-off abdominal ultrasound scan that is offered to all men at the age of 65 years.

Men who are found to have an AAA of at least 3cm in maximum diameter are surveyed with serial abdominal ultrasound scans in the community or at a local hospital.

Those patients whose aneurysms are found to have increased in size beyond 5cm will be referred to the regional vascular service for consideration for surgical repair.

Case study

A 72-year-old man experienced abdominal and back pain while at home. He was previously known to have hypertension that was treated with medication, but he was otherwise in excellent health.

The patient called his GP practice and was advised to call the emergency services. He was taken to A&E and after initial assessment and investigations, was found to have a leaking AAA. The hospital did not have a vascular service, so the patient was transferred to the regional vascular service. While in transit, he experienced further pain followed by loss of consciousness. He received standard resuscitation measures in transit and in A&E; however, he died before receiving surgical intervention. At postmortem, a 7cm leaking AAA was identified as the cause of death.

If a screening programme had been in place for this patient, an abdominal ultrasound scan at the age of 65 would have identified the AAA and he would have received elective surgery to repair it. His death from a leaking AAA was therefore very much avoidable.

Mr Kyriakides is consultant vascular and endovascular surgeon at The London Clinic